Well, first of all, you need to somehow administer the LSD dose. From a tactical perspective, the coffee makes sense.

Second of all LSD, has a bit of a stimulant "excitable" effect. So you might want to give them Decaf to compensate. You're right that it's a confounding variable though, and there's a good chance that people like me would be less productive because of the decaf, especially if the LSD dose was too small. https://erowid.org/chemicals/lsd/lsd_effects.shtml

The variable is just the lsd. Caffeine is constant in both control and experimental groups. Plus the organisms would most likely exhibit caffeine seeking behavior anyhow.

> One group gets decaf coffee with an LSD microdose > One group gets normal coffee.

Fun fact: The first time the Beatles did LSD, they were unknowingly dosed by their dentist.

Fortunately (according to [0]) they were told about it before the dose kicked in.

0) https://www.vice.com/en_us/article/the-oral-history-of-the-b...

Yep. In their coffee, in fact.